Showing papers by "Paul Sabatier University published in 2000"

The Sloan Digital Sky Survey: Technical summary

Abstract: The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and nonluminous matter in the universe: a photometrically and astrometrically calibrated digital imaging survey of π sr above about Galactic latitude 30° in five broad optical bands to a depth of g' ~ 23 mag, and a spectroscopic survey of the approximately 106 brightest galaxies and 105 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS and serves as an introduction to extensive technical on-line documentation.

Guidelines for using human event-related potentials to study cognition: Recording standards and publication criteria

Abstract: Event-related potentials ~ERPs! recorded from the human scalp can provide important information about how the human brain normally processes information and about how this processing may go awry in neurological or psychiatric disorders. Scientists using or studying ERPs must strive to overcome the many technical problems that can occur in the recording and analysis of these potentials. The methods and the results of these ERP studies must be published in a way that allows other scientists to understand exactly what was done so that they can, if necessary, replicate the experiments. The data must then be analyzed and presented in a way that allows different studies to be compared readily. This paper presents guidelines for recording ERPs and criteria for publishing the results.

Nuclear gene OPA1, encoding a mitochondrial dynamin-related protein, is mutated in dominant optic atrophy.

Abstract: Optic atrophy type 1 (OPA1, MIM 165500) is a dominantly inherited optic neuropathy occurring in 1 in 50,000 individuals that features progressive loss in visual acuity leading, in many cases, to legal blindness. Phenotypic variations and loss of retinal ganglion cells, as found in Leber hereditary optic neuropathy (LHON), have suggested possible mitochondrial impairment. The OPA1 gene has been localized to 3q28-q29 (refs 13-19). We describe here a nuclear gene, OPA1, that maps within the candidate region and encodes a dynamin-related protein localized to mitochondria. We found four different OPA1 mutations, including frameshift and missense mutations, to segregate with the disease, demonstrating a role for mitochondria in retinal ganglion cell pathophysiology.

Connectivity of growing random networks.

Abstract: A solution for the time- and age-dependent connectivity distribution of a growing random network is presented. The network is built by adding sites that link to earlier sites with a probability A(k) which depends on the number of preexisting links k to that site. For homogeneous connection kernels, A(k) approximately k(gamma), different behaviors arise for gamma 1, and gamma = 1. For gamma 1, a single site connects to nearly all other sites. In the borderline case A(k) approximately k, the power law N(k) approximately k(-nu) is found, where the exponent nu can be tuned to any value in the range 2

Inspiration for optimization from social insect behaviour

Abstract: Research in social insect behaviour has provided computer scientists with powerful methods for designing distributed control and optimization algorithms. These techniques are being applied successfully to a variety of scientific and engineering problems. In addition to achieving good performance on a wide spectrum of 'static' problems, such techniques tend to exhibit a high degree of flexibility and robustness in a dynamic environment.

Building‐block approach for determining low‐frequency normal modes of macromolecules

Abstract: Normal mode analysis of proteins of various sizes, ranging from 46 (crambin) up to 858 residues (dimeric citrate synthase) were performed, by using standard approaches, as well as a recently proposed method that rests on the hypothesis that low-frequency normal modes of proteins can be described as pure rigid-body motions of blocks of consecutive amino-acid residues. Such a hypothesis is strongly supported by our results, because we show that the latter method, named RTB, yields very accurate approximations for the low-frequency normal modes of all proteins considered. Moreover, the quality of the normal modes thus obtained depends very little on the way the polypeptidic chain is split into blocks. Noteworthy, with six amino-acids per block, the normal modes are almost as accurate as with a single amino-acid per block. In this case, for a protein of n residues and N atoms, the RTB method requires the diagonalization of an n x n matrix, whereas standard procedures require the diagonalization of a 3N x 3N matrix. Being a fast method, our approach can be useful for normal mode analyses of large systems, paving the way for further developments and applications in contexts for which the normal modes are needed frequently, as for example during molecular dynamics calculations.

Photoluminescence properties of silicon nanocrystals as a function of their size

Abstract: We present results on the photoluminescence (PL) properties of silicon nanocrystals as a function of their size. The nanocrystals are synthesized by laser pyrolysis of silane in a gas flow reactor and deposited at low energy on a substrate after a mechanical velocity and size selection. Both the photoluminescence spectroscopy and yield have been studied as well as the effect of aging of the samples in air. The measurements show that the PL of the silicon nanocrystallites follows the quantum confinement model very closely. The apparent PL yields are rather high (up to 18%). From evaluation of the size distribution obtained by atomic force microscopy it is concluded that the intrinsic PL yield of the nanocrystals can reach almost 100%. These results enabled us to develop a simple theoretical model to describe the PL of silicon nanocrystals. This model can also explain the changes of PL with aging of the sample, just by invoking a decrease of the size of the crystalline core as a result of oxidation.

Branching and interacting particle systems. Approximations of Feynman-Kac formulae with applications to non-linear filtering

Abstract: This paper focuses on interacting particle systems methods for solving numerically a class of Feynman-Kac formulae arising in the study of certain parabolic differential equations, physics, biology, evolutionary computing, nonlinear filtering and elsewhere. We have tried to give an “expose” of the mathematical theory that is useful for analyzing the convergence of such genetic-type and particle approximating models including law of large numbers, large deviations principles, fluctuations and empirical process theory as well as semigroup techniques and limit theorems for processes.

Use of the “Odds Ratio” for Diagnosing Forecast Skill

Abstract: This study investigates ways of quantifying the skill in forecasts of dichotomous weather events. The odds ratio, widely used in medical studies, can provide a powerful way of testing the association between categorical forecasts and observations. A skill score can be constructed from the odds ratio that is less sensitive to hedging than previously used scores. Furthermore, significance tests can easily be performed on the logarithm of the odds ratio to test whether the skill is purely due to chance sampling. Functions of the odds ratio and the Peirce skill score define a general class of skill scores that are symmetric with respect to taking the complement of the event. The study illustrates the ideas using Finley’s classic set of tornado forecasts.

Hydrogen in nominally anhydrous upper-mantle minerals concentration levels and implications

Abstract: Several of the supposedly anhydrous major minerals of the upper mantle have been shown to regularly contain small amounts of hydrogen. The concentrations measured in the most important minerals obtained from mantle xenoliths are, expressed in ppm H 2 O, 100-1300 for clinopyroxene, 60-650 for orthopyroxene, 0- 140 for olivine and 1-200 for garnet. Hydrogen is normally structurally incorporated as hydroxyl ions, and in many cases the hydrogen ions seem to act as charge compensators associated with point defects, such as metal vacancies or substitution by mono- or trivalent cations. The determination of the exact amount of hydrogen stored in these nominally anhydrous upper mantle minerals is a key-step toward quantification of the water content of the mantle, as well as understanding of its internal water cycle. For instance, a concentration of 100 ppm H 2 O homogeneously distributed within the upper mantle above 410 km depth is approximately equivalent to a 100 m water layer at the Earth9s surface. However, the relatively fast kinetics of dehydrogenation with concomitant oxidation of iron within these minerals, implies that hydrogen as well as Fe 3+ concentrations in equilibrium with mantle conditions might be different from those measured from recovered xenolith samples. High-pressure experimental measurements of hydrogen solubility as a function of PH 2 O show a trend similar to the hydrogen contents of natural samples, with hydrogen saturation levels that decrease following the mineral series: diopside > enstatite > olivine > pyrope. Except pyrope, these minerals may incorporate more than 1000 ppm H 2 O. Based on recent data of water solubility, stability and partitioning, we suggest that an entire upper mantle saturated in hydrogen is highly unprobable and that the maximum average amount of hydrogen stored in the nominally anhydrous minerals of the upper mantle is around 600 ppm H 2 O. Despite the important progress achieved during the last years, our knowledge of the concentration of hydrogen stored as point defects in the mantle above 410 km is still too poorly constrained. The importance of nominally anhydrous minerals for the water budget of the upper mantle is now well established but still awaits complete quantification.

Transition from glow silent discharge to micro-discharges in nitrogen gas

Abstract: At atmospheric pressure, the electrical breakdown of a silent discharge can occur in many thin filaments (leading to micro-discharges) or in a single discharge canal covering the entire electrode surface (leading to a glow discharge). The aim of this paper is to contribute to a better understanding of the transition from a glow silent discharge to micro-discharges in nitrogen at atmospheric pressure. For this purpose, the two types of regime have been studied by emission spectroscopy and electrical measurements. The transition is always observed due to an increase of the power dissipated in the gas gap, but the maximum power that can be used while maintaining a glow discharge depends on the nature of the dielectric surface in contact with the gas. These results have been explained by the predominance of the density of metastable nitrogen molecules on the discharge regime. Due to the creation of seed electrons via Penning ionization, these metastable molecules can control the gas breakdown and so the discharge regime. Their density essentially depends on their quenching rate. The products etched from the surfaces in contact with the discharge appear to be the main source of the metastable molecules quenching. Therefore, the nature of the surface controls the nature of the quenching of the metastable molecules and the power dissipated in the discharge the quencher density.

From Brunn-Minkowski to Brascamp-Lieb and to logarithmic Sobolev inequalities

Abstract: We develop several applications of the Brunn—Minkowski inequality in the Prekopa—Leindler form. In particular, we show that an argument of B. Maurey may be adapted to deduce from the Prekopa—Leindler theorem the Brascamp—Lieb inequality for strictly convex potentials. We deduce similarly the logarithmic Sobolev inequality for uniformly convex potentials for which we deal more generally with arbitrary norms and obtain some new results in this context. Applications to transportation cost and to concentration on uniformly convex bodies complete the exposition.

Ferrocene and ferrocenyl derivatives in luminescent systems

Abstract: Owing to their fairly high stability under visible irradiation, ferrocene and ferrocenyl derivatives are widely used in luminescent systems. They are classical quenchers of excited states. Both energy and electron transfer may be involved, depending on the nature of the excited species. Inter- or intramolecular quenching are encountered. Applications span from the study of reaction mechanisms to that of organized or biological media. Recently, dyads and polyads designed for their ability to mimic photosynthetic centers or for their photodiode properties have also been obtained. Finally, the incorporation of a ferrocenyl derivative in a luminescent system does not necessarily lead to luminescence quenching. New applications are emerging, in which advantage is taken of the presence of ferrocene acting as a redox center: this gives optically and electrochemically active sensors. The present review encompasses the literature up to November 1999.

Synthesis of single-walled carbon nanotube–Co–MgO composite powders and extraction of the nanotubes

Abstract: A carbon nanotube–Co–MgO composite powder is prepared by reducing a Mg0.9Co0.1O solid solution in H2–CH4 atmosphere. The oxide matrix and part of the Co catalyst are dissolved by acid treatment without damage to the nanotubes. More than 80% of the carbon nanotubes have either one or two walls. The diameters of the nanotubes are in the range 0.5–5 nm. The utilized method may be a real improvement in the low-cost, large-scale synthesis of single- and double-walled carbon nanotubes.

Autoregressive Forecasting of Some Functional Climatic Variations

Abstract: Many variations such as the annual cycle in sea surface temperatures can be considered to be smooth functions and are appropriately described using methods from functional data analysis. This study defines a class of functional autoregressive (FAR) models which can be used as robust predictors for making forecasts of entire smooth functions in the future. The methods are illustrated and compared with pointwise predictors such as SARIMA by applying them to forecasting the entire annual cycle of climatological El Nino- Southern Oscillation (ENSO) time series one year ahead. Forecasts for the period 1987-1996 suggest that the FAR functional predictors show some promising skill, compared to traditional scalar SARIMA forecasts which perform poorly.

Extended magnetic reconnection at the Earth's magnetopause from detection of bi-directional jets

Abstract: Magnetic reconnection is a process that converts magnetic energy into bi-directional plasma jets; it is believed to be the dominant process by which solar-wind energy enters the Earth's magnetosphere1,2. This energy is subsequently dissipated by magnetic storms and aurorae3,4. Previous single-spacecraft observations5,6,7 revealed only single jets at the magnetopause—while the existence of a counter-streaming jet was implicitly assumed, no experimental confirmation was available. Here we report in situ two-spacecraft observations of bi-directional jets at the magnetopause, finding evidence for a stable and extended reconnection line; the latter implies substantial entry of the solar wind into the magnetosphere. We conclude that reconnection is determined by large-scale interactions between the solar wind and the magnetosphere, rather than by local conditions at the magnetopause.

'Hard' women and 'soft' women. The social construction of identities among female boxers

Abstract: This article uses a combination of Bourdieu's concept of habitus theory and an interactionist perspective to examine women's participation in the traditionally `man's world' of boxing. The two major aims of the study were to identify how women entered and stayed involved in boxing and the types of identities that they forged in the process. The data were collected via participant-observation and in-depth interviews with a sample of women boxers and their coaches. It was found that the women's entry into and continued involvement in boxing depends on both disposition and situation. It was also concluded that women boxers occupied an ambivalent position: on the one hand, by definition, they challenged the existing gender order; on the other hand, they also reinforced the status quo by displaying traditional modes of femininity. This tension was related to the modalities of boxers' practice (`hard' or `soft') and their social histories. In short, the process of identity-formation among women boxers was insep...

Cross-regulation of competence pheromone production and export in the early control of transformation in Streptococcus pneumoniae.

Abstract: Two operons, comAB and comCDE, play a key role in the co-ordination of spontaneous competence development in cultures of Streptococcus pneumoniae. ComAB is required for export of the comC-encoded competence-stimulating peptide (CSP). Upon CSP binding, the histidine kinase ComD activates ComE, its cognate response regulator, required for autoinduction of comCDE and for induction of the late competence genes. To understand better the early control of competence development, mutants upregulating comCDE (ComCDEUP) were isolated using a comC-lacZ transcriptional fusion. Mutants were generated by polymerase chain reaction mutagenesis of the comCDE region and by in vitro transposon mutagenesis of the chromosome. Both types of ComCDEUP mutants exhibited similar phenotypes. They differed from wild type in displaying trypsin-resistant transformation, competence under acid growth conditions and expression of comCDE under microaerobiosis; increased production of CSP in the mutants could account for the various phenotypes. The ComCDEUP transposon mutations included four independent insertions in the ciaR gene, which encodes the response regulator of a two-component system previously found to affect competence, and two immediately upstream of the comAB operon. The latter two resulted in comAB overexpression, indicating that CSP export is rate limiting. Among comDE point mutations, a single amino acid change in ComD (T233I) conferred constitutive, CSP-independent competence and resulted in comAB overexpression, providing support for the hypothesis that ComE regulates comAB; a ComE mutant (R120S) exhibited altered kinetics of competence shut-off. Collectively, these data indicate that pheromone autoinduction, cross-regulation of the comAB and comCDE operons and, possibly, competence shut-off contribute to the early control of competence development in S. pneumoniae. They argue for a metabolic control of competence, mediated directly or indirectly by CiaR, and they suggest that both comAB and comCDE are potential targets for regulation.